The present invention generally concerns corn milling processes and machines. The invention specifically concerns multiple corn product milling processes and machines.
There are two primary types of corn processing conducted presently, dry grind and wet milling processes. The wet milling processes are efficient in their use of corn since they produce numerous high value corn products, such as corn oil, starch, corn gluten meal, corn gluten feed, and corn steep liquor. However, the wet milling processes require very high capital investments in machinery. Dry grind processes are used to produce ethanol and animal feed. Animal feed is substantially less valuable than corn oil and zein, which are left in the animal feed produced by a dry mill process. A reason for existence of the dry grind plants to date has been government ethanol subsidies, which are likely to disappear.
Some methods to extract oil and zein from dry mill corn have been proposed in the literature, but have yet to demonstrate efficiency meeting commercial production requirements. One type of proposed method is embodied in U.S. Pat. No. 4,716,218 and a xe2x80x9cSequential Extraction Processxe2x80x9d developed at Iowa State University. This type of method uses ethanol to extract oil and zein. Evaporation is required to remove the ethanol, and then hexane-extraction to separate the oil from the zein with further subsequent evaporation of the hexane from the oil. These are relatively complicated processes. They are also expensive due to their energy intensive nature. Significant heating requirements result from the multiple required evaporations. Further, the evaporations create pollution concerns.
Another proposed method to remove oil from dry-milled corn is mechanical degermination. This method produces corn germ with less than approximately 50 percent oil. The germ must be subsequently processed to recover the oil. No ability to recover zein is presented by this method, however, and there is no known utilization of the method to obtain corn oil and zein in a manufacture scaled product.
Thus, there is a need for an improved method capable of using dry grind corn, as well as wet milled corn product, to produce multiple corn products of value. It is an object of the invention to provide such a method. It is a further object of the invention to provide a method for extracting corn oil and protein, which method is capable of utilizing dry grind corn or wet milled corn product through ethanol treatment with filtration.
The method of the present invention obtains valuable oil and zein from various forms of corn to meet or exceed such needs. Membranes are relied up to filter valuable oils and proteins. Input to the corn process of the invention is corn of multiple forms. Ethanol is the only reagent utilized by the process, and conventional dry and wet mill plants therefore already provide the necessary reagent supply for implementation of the invention. The invention therefore serves as the basis for an add on technology to existing dry mill or wet mill plant, as well as the basis upon which new dry mill and wet plants may be constructed. Dry mill plants are likely to benefit the most from the invention, since the invention provides ways to extract more valuable corn oils and proteins from the corn while making use of the basic dry mill equipment and products of conventional dry mill plants.
A plant modified or constructed to implement the process of the invention uses high concentration ethanol, approximately 90-100% ethanol, to separate oil from the corn. The corn may be in any form, e.g., wet mill product, dry flakes, dry particles, or whole kernels. Alternatively or additionally, zein protein may be partially or substantially extracted using an ethanol extraction step with an ethanol concentration between approximately 60 and 90%. The ethanol solution containing the extracted product is separated from other corn solids by filtration or centrifugation. Synthetic semipermeable membranes are used to separate zein from the oil, producing relatively pure oil and/or pure zein. Additional membrane filtration is used to concentrate the oil and/or zein, and to recover the ethanol for further use in processing, if desired. Recycled ethanol may then be used in additional extraction of oil and/or zein, or may be used in a distillation operation if ethanol product is also being produced by the plant.